Kynurenic Acid in Honey from Arboreal Plants: MS and NMR Evidence

KYNA, a Trp metabolite, shows neuroprotective activity against excitotoxic amino acids by antagonizing the NMDA receptor (glycine, glutamate). Here we report the identification of KYNA by a combination of ESI-MS/MS and 1D- and 2D-NMR analyses in honey varieties of arboreal origin. KYNA are absent in single-flower honeys from herbal flowers. These different distribution patterns might possibly involve an indirect plant defence mechanism against fungal pathogens and herbivorous parasites, ever-present on wild trees. The presence of KYNA in honey may explain its pain-relieving effects reported in the literature. The substance, acting in concert with honey flavonoids (COX-2 inhibitors), by antagonizing the NMDA receptor may contribute to the antinociceptive effect of honey. Moreover, kynureninates, owing to their antimicrobial properties, can favour the successful outcome of wounds and burns. Abbreviations CID:collision-induced decomposition COSY:correlation spectroscopy COX-2:cyclo-oxygenase-2 DMSO:dimethyl sulfoxide ESI-MS:electrospray ionisation mass spectrometry HETCOR:hetero-correlation HMBC:heteronuclear multiple bond correlation HMQC:heteronuclear multiple quantum correlation IL:interleukin KYNA:kynurenic acid NMDA: N -methyl-d-aspartic acid QUIN:quinoline RP-SPE:reverse-phase solid phase extraction Trp: tryptophan